1 Definition, Purpose and Significance
Water resistance refers to the resistance of the paint film to the action of water. That is, under the specified conditions, soak the painted test panel in water, observe whether it has whitening, loss of light, blistering, falling off, etc., and the difficulty of restoring the original state.
Coatings are often in direct contact with humid air or water in practical applications. With the expansion and water permeability of the paint film, various damage phenomena such as blistering , which directly affect the service life of the coating. , so for certain coating products. A water resistance test is required. The water resistance of the paint film is often related to factors such as the polar groups contained in the resin, the water-soluble salts in the pigment, and various additives in the coating film. It is also affected by the surface of the coated object and the coating film. Influenced by factors such as drying conditions.
2 Relevant standards
GB/T 1733_93 Determination of water resistance of paint film
GB/T 5209_85 Determination of water resistance of paints and varnishes Water immersion method
3 Introduction to key points of inspection methods
3.1 GB/T1733-93 Determination of water resistance of paint film
3.1.1 Test Principle
Immerse the sample in normal temperature water or boiling water, and evaluate the water resistance of the paint film by observing the surface changes of the paint film after the specified test time.
3.1.2 Materials and equipment
glass sink;
Substrate: tinplate;
Plain water or deionized water (in line with the requirements of third-grade water);
Level 3 Water Requirements · pH Range (25°C) 5.0～7.5
Conductivity (25℃) mS/m ≤0.50
3.1.3 Operation points
3.1.3.1 Normal temperature water immersion test method
Unless otherwise specified, a 1:1 mixture of paraffin wax and rosin should be applied to the edges of the test panels before testing, and the edge sealing width should be 2 to 3 mm.
Fill a glass sink with distilled or deionized water. Unless otherwise specified, adjust the water temperature to (23 ± 2) °C and maintain this temperature throughout the test. Put three test panels into it, and soak 2/3 of the length of each test panel in sub-water.
When the immersion time specified in the product standard is reached, take the test panel out of the tank, blot it dry with filter paper, check the test panel visually immediately or after adjusting according to the time state specified in the product, and record whether it loses light or changes color , Blistering, wrinkling, shedding, rusting and other phenomena and recovery time.
3.1.3.2 Boiling water test method
The whole test process is the same as 3.1-3.1, the difference is that the sample is immersed in water that is kept boiling.
3.1.4 Evaluation of results
At least two of the three test panels shall meet the requirements of the product standard to be qualified.
3.2 GB/T 5209-85 Determination of water resistance of paints and varnishes Water immersion method
3.2.1 Test principle
This method is to assess the performance index of the damage results caused by the presence of condensed water in the paint film, and it is an accelerated damage test method.
3.2.2 Materials and equipment
Test equipment: All parts in contact with the test water shall be made of inert materials.
3.2.3 Operation points
The back and sides of the test panels shall be painted with a protective paint that does not contain dimethicone or any other similar water-soluble pigments. There should be no effect on the test results after painting. The edge width is 2-3mm.
Add a sufficient amount of deionized water that meets the requirements into the tank, keep three-quarters of the sample soaked in hand water, and then open the water circulation or ventilation in the tank. Adjust the water temperature to (40 ± 1 ) °C and maintain this temperature throughout the test. Take a sample to check the conductivity of the water in the tank so that it is not greater than 2µS/cm. (Related instruments: constant temperature Water Tank)
The test panels that have been operated and placed according to the regulations shall be inspected before the test and recorded, and then placed on the test rack to keep the distance between the test panels at least 30mm and the distance between the test panels and the tank bottom and wall at least 50mm. During the test, the position of the test plate in the well should be constantly changed, and the time interval between the changes of the position shall not exceed 3d.
If it is stipulated that an intermediate inspection is to be carried out during the test period, the test panel shall be taken out of the tank, blotted with filter paper to dry up the water traces, check for damage immediately, and then put it back into the tank immediately. The inspection shall be carried out according to the relevant documents.
At the end of the specified period, the test panel should be taken out from the tank, and the damage can be checked by drying the water with makeup paper. However, when inspecting the indicators such as reduced adhesion, brittleness, discoloration, loss of gloss, and rust after the paint film is tested, the test panel should be moved into a constant temperature and humidity room for 24 hours before inspection.
Use a non-corrosive paint remover to carefully remove a 150mmx30mm paint film on the surface of the test panel to expose the substrate and check the exposed metal corrosion. For reference, the exposed part should be protected with a suitable transparent paint.
3.2.4 Result Judgment
Record the blistering, wrinkling, rusting, loss of gloss, discoloration, peeling off, decreased adhesion of the test panel and the rustiness of the substrate after paint removal. The damage phenomenon within 8mm of the edge of the test plate and the obvious damage caused by man are not included in the test results.
3.3 The main factors affecting the water resistance of the paint film
3.3.1 Inappropriate selection of substrate or unreasonable treatment of substrate will affect the water resistance of the paint film. For the selection of asbestos cement board as the substrate, special attention should be paid to the acidity, alkalinity and density of the substrate.
3.3.2 Due to the unreasonable preparation process, the paint film will produce air bubbles, shrinkage cavities and other pathological conditions, which will affect the water resistance of the paint film. The uneven thickness of the paint film will also affect the water resistance of the paint film.
3.3.3 Drying process: Improper drying conditions and insufficient drying time will greatly affect the water resistance of the paint film. (Related Instrument: Drying Time Meter)
3.3.4 Test water quality: The test water does not meet the requirements of third-grade water, and it is not suitable for some users to use tap water or pure water as test water.
3.4 See Table 4 for the comparison of the two standards.
